Camera

ABSTRACT

A camera includes: a first sensor of a storage type that has a plurality of pixels; a focus detection unit that detects a focus adjustment state of a photographic optical system based upon a detection signal from the first sensor for a photographic subject; a second sensor that acquires an image of the photographic subject; an extraction unit that extracts a main photographic subject region from image information acquired by the second sensor; and a control unit that controls accumulation of electrical charge by the first sensor, based upon values outputted from pixels of the first sensor that correspond to the main photographic subject region.

INCORPORATION BY REFERENCE

The disclosure of the following priority application is hereinincorporated by reference:

Japanese Patent Application No. 2007-192180 filed Jul. 24, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a camera that performs focus detection.

2. Description of Related Art

A technique is known for detecting the defocus amount of a photographicoptical system of a camera or the like based upon the detection signalfrom a storage-type sensor that has a plurality of pixels (refer toJapanese Laid-Open Patent Publication Heisei 5-249369).

SUMMARY OF THE INVENTION

When determining the accumulation time period of a storage type sensorin the prior art, an accumulation time period is determined that issuitable for the high luminance portion of the photographic field. Dueto this, if the luminance of the main photographic subject is low, thereis a fear that the detection signal from such a storage type sensor willbe undesirably flattened.

According to the 1st aspect of the present invention, a cameracomprises: a first sensor of a storage type that has a plurality ofpixels; a focus detection unit that detects a focus adjustment state ofa photographic optical system based upon a detection signal from thefirst sensor for a photographic subject; a second sensor that acquiresan image of the photographic subject; an extraction unit that extracts amain photographic subject region from image information acquired by thesecond sensor; and a control unit that controls accumulation ofelectrical charge by the first sensor, based upon values outputted frompixels of the first sensor that correspond to the main photographicsubject region.

According to the 2nd aspect of the present invention, in the cameraaccording to the 1st aspect, it is preferred that the extraction unitextracts the main photographic subject region by deciding whether or notat least one of a hue and a luminance is approximately equal to eachother between an upper end region and another region in a direction fromabove towards below in the image information.

According to the 3rd aspect of the present invention, in the cameraaccording to the 1st aspect, it is preferred that the first sensor isconstituted by a line sensor.

According to the 4th aspect of the present invention, in the cameraaccording to the 3rd aspect, it is preferred that the focus detectionunit performs focus detection calculation by a phase detection method inwhich a defocus amount is calculated according to a gap between a pairof images given by the detection signal of the line sensor.

According to the 5th aspect of the present invention, in the cameraaccording to the 1st aspect, it is preferred that the second sensor isconstituted by an area sensor for photometry.

According to the 6th aspect of the present invention, in the cameraaccording to the 1st aspect, it is preferred that the control unitcontrols accumulation of electrical charge by the first sensor, so thatoutput values of pixels of the first sensor that correspond to the mainphotographic subject region that has been extracted approach apredetermined target level.

According to the 7th aspect of the present invention, in the cameraaccording to the 6th aspect, it is preferred that the predeterminedtarget level is a level that is lower than a saturation level and isclose to the saturation level.

According to the 8th aspect of the present invention, a cameracomprises: a first sensor of a storage type that has a plurality ofpixels; a focus detection unit that detects a focus adjustment state ofa photographic optical system based upon a detection signal from thefirst sensor for a photographic subject; a second sensor that acquiresan image of the photographic subject; an extraction unit that extracts amain photographic subject region from image information acquired by thesecond sensor; a control unit that controls accumulation of electricalcharge by the first sensor, based upon values outputted from pixels ofthe first sensor that correspond to the main photographic subjectregion; and a third sensor that acquires an image of the photographicsubject for recording.

According to the 9th aspect of the present invention, in the cameraaccording to the 8th aspect, it is preferred that the control unitperforms control of electric charge accumulation by the first sensor andacquisition of an image of the photographic subject by the secondsensor, before performing acquisition of an image of the photographicsubject with the third sensor.

According to the 10th aspect of the present invention, a camera controlmethod comprises: capturing an image; extracting a main photographicsubject region from the captured image; and determining a sensitivity ofa range-finding sensor having a plurality of pixels, based upon outputsof pixels of the range-finding sensor that correspond to the extractedmain photographic subject region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figure for explanation of the structure of the main portionsof a single lens reflex electronic camera that is an embodiment of thepresent invention;

FIG. 2 is a block diagram showing an example of a circuit structure ofthis single lens reflex electronic camera;

FIG. 3 is a flow chart for explanation of the flow of photographicprocessing performed by a calculation device;

FIG. 4 is a figure showing an example of an image of a photographicsubject that is being imaged upon an area sensor;

FIG. 5 is a figure showing an example of an image acquired by the areasensor by capturing the photographic subject image of FIG. 4;

FIG. 6 is a figure showing an example of a situation in which the imageof the photographic subject is divided into two regions; and

FIG. 7 is a figure showing an example of the relative positionalrelationship between light reception areas of a range-finding sensor andthe light reception area of the area sensor.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, preferred embodiments for implementation of thepresent invention will be explained with reference to the drawings. FIG.1 is a figure for explanation of the structure of the main portions of asingle lens reflex electronic camera according to an embodiment of thepresent invention. In FIG. 1, a photographic lens 150 is installed to acamera main body 100 and is made so as to be detachable therefrom.

Light from a photographic subject 101 is incident upon the camera mainbody 100 via optical systems 151 and 152 and an aperture 153 of thephotographic lens 150. Before a release button (not shown in thefigures) is actuated, this photographic subject light that is incidentupon the camera main body 100 is conducted upwards by a quick returnmirror 103 to a viewfinder section and is imaged upon a viewfinderscreen 104.

This photographic subject light that is imaged upon the viewfinderscreen 104 is also incident upon a roof pentaprism 105. On the one hand,this roof pentaprism 105 conducts this incident photographic subjectlight to an eyepiece optical system 112, and on the other hand it alsoconducts a portion thereof to an area sensor imaging optical system 106.This area sensor imaging optical system 106 re-images an image of thephotographic subject upon an area sensor 107. The area sensor 107outputs to a calculation device 107 a photoelectric conversion signalthat corresponds to the brightness of this image of the photographicsubject. The area sensor 107 is constituted by a CCD image sensor or thelike that has a plurality of photographic conversion elements thatcorrespond to pixels, but its light reception surface has a smallernumber of pixels than does that of an image sensor 121 that will bedescribed hereinafter.

On the other hand, a portion of the photographic subject light that isincident upon the camera main body 100 passes through the quick returnmirror 103 and is conducted to a range-finding sensor 109 below asub-mirror 108. The range-finding sensor 109 outputs a photoelectricconversion signal that corresponds to the brightness of the image of thephotographic subject to a focus detection device 134 (see FIG. 2) thatwill be described hereinafter. The range-finding sensor 109 isconstituted by a CCD line sensor having a plurality of photoelectricconversion elements that correspond to pixels. The detection signal fromthe range-finding sensor 109 is used for detecting the state of focusadjustment by the photographic lens 150.

After the release button (not shown in the figures) is depressed, thequick return mirror 103 rotates upwards out of the optical path, and thelight from the photographic subject is conducted via a shutter 113 to animage sensor 121, so that an image of the photographic subject is imagedupon the photographic image surface thereof. This image sensor 121 isconstituted by a CCD image sensor or the like having a plurality ofphotoelectric conversion elements that correspond to pixels. The imagesensor 121 captures the image of the photographic subject that is imagedupon its photographic image surface, and outputs a photoelectricconversion signal that corresponds to the brightness of thisphotographic subject image.

FIG. 2 is a block diagram showing an example of a circuit structure ofthe-above described single lens reflex electronic camera. A timinggenerator (TG) 125 generates a timing signal according to a commandoutputted from a calculation device 110, and supplies a timing signal toeach of a driver 124, and AFE (Analog Front End) circuit 122, and an A/Dconversion circuit 123. The driver 124 causes the image sensor 121 toaccumulate electric charges, generates a drive signal for dischargingthe accumulated charges by using the timing signal described above, andsupplies this drive signal that it has generated to the image sensor121.

The AFE (Analog Front End) circuit 122 performs analog processing (gaincontrol or the like) upon the photoelectric conversion signals (theaccumulated electric charges) outputted from the image sensor 121. Andthe A/D conversion circuit 123 converts the image capture signal afteranalog processing to a digital signal.

The calculation device 110 is constituted by a micro computer or thelike, and inputs signals that are outputted from various blocks thatwill be described hereinafter, performs predetermined calculationsthereupon, and outputs control signals to various blocks based upon theresults of these calculations.

A half press switch 130 and a full press switch 131 are operated bydepression actuation of the release button (not shown in the figures),and each of them outputs ON signal to the calculation device 110. The ONsignal from the switch 130 is outputted when the release button (notshown in the figures) is actuated by being pressed downwards as far as alevel of half of its normal stroke, and its output may be cancelled byrelease of this half stroke pressing down actuation. And the ON signalfrom the switch 131 is outputted when the release button (not shown inthe figures) is actuated by being pressed downwards through its normalstroke, and its output may be cancelled by release of this normal strokepressing down actuation.

Actuation members 125 output setting and changeover signals thatcorrespond to various types of setting actuations and selectionactuations to the calculation device 110. In these actuation members 125there are included: an actuation member that selects photographic modeand the like; actuation members that set image capture sensitivity (ISOsensitivity), exposure calculation mode (program auto, aperture priorityauto, shutter speed priority auto, and the like) and so on; a cruciformswitch that outputs a signal indicating its actuation direction; a mainswitch; and so on.

The focus detection device 134 includes the range-finding sensor 109described above (see FIG. 1). The focus detection device 134 calculatesa focus adjustment state (a defocus amount) for the photographic lens150 using the detection signal of the range-finding sensor 109, andcalculates a shift amount of the optical system 152 for focus adjustmentaccording to the result of this calculation.

In concrete terms, the focus detection device 134 obtains a deviationamount of relative position (a relative gap) between two images that areimaged upon the line sensor in different positions, these images beingformed by a pair of ray bundles for defocus amount detection that areincident via different regions of the photographic lens 150. This pairof images of the photographic subject are close to one another in the socalled front-focus state in which the photographic lens 150 focuses aclear image of the photographic subject in front of its expected focusplane, and, conversely, are far away from one another in the so-calledreae-focus state in which the photographic lens 150 focuses a clearimage of the photographic subject behind its expected focus plane. Whenthe two images that are imaged in different positions upon the linesensor are overlapped to one another, then, in the focused state inwhich a clear image of the photographic subject is focused upon thepredetermined focus plane, the above described pair of images agree withone another. Accordingly the focus adjustment state of the photographiclens 150, in other words the defocus amount, may be obtained byobtaining the deviation amount of relative position between the pair ofimages. And a calculation circuit within the focus detection device 134determines the forwards or backwards shift amount and the shiftdirection of the focus adjustment optical system 152 according to thedefocus amount, and transmits the data required for driving the opticalsystem 152 to the photographic lens 150 via the calculation device 110and a communication and control unit 136.

The photometric unit 135 includes the area sensor 107 (see FIG. 1). Thisphotometric unit 135 calculates the luminance of the photographicsubject using the detection signal (i.e. the image capture signal) ofthe area sensor 107. The photometric unit 135 further performsconventional exposure calculation using the image capture sensitivitythat is set, lens information that is received via the communicationcontrol unit 136, and the photographic subject luminance that has beencalculated, and thereby determines a control exposure. As for theexposure calculation mode, this is performed according to an exposurecalculation mode that corresponds to an actuation signal from theactuation members 125.

The communication control unit 136 performs communication with thephotographic lens 150 that is attached to the camera main body 100, andan external device (a personal computer or the like) that is connectedthereto by wireless or cable connection. While on the one hand, bycommunication between the camera main body 100 and the photographic lens150, lens information such as the aperture value and lens data and so onis transmitted from the photographic lens 150 to the camera main body100, also on the other hand lens control information such as the shiftamount and a drive command for the above described focus adjustmentoptical system 152 and the like are transmitted from the camera mainbody 100 to the photographic lens 150.

By communication between the camera main body 100 and the externaldevice, on the one hand maintenance information and program data and soon may be transmitted from the external device to the camera main body100, and on the other hand maintenance information and photographicimage data and so on may be transmitted from the camera main body 100 tothe external device.

A shutter control unit 137 performs charge and drive control of theshutter 113 (see FIG. 1) according to commands that are outputted fromthe calculation device 110. And, according to commands that areoutputted from the calculation device 110, a mirror control unit 138controls mirror up driving of the quick return mirror 103 (i.e. makingit retract upwards out of the optical path in FIG. 1), and mirror downdriving thereof (i.e. making it return to its position shown in FIG. 1).

The calculation device 110 performs image processing. This calculationdevice 110, apart from performing white balance processing and the likeupon the image data after digital processing, also performs compressionprocessing to compress the image data in a predetermined format,decompression processing to decompress image data that has beencompressed, and the like.

A display image generation circuit 128 creates display data for displayupon a liquid crystal monitor 129. The liquid crystal monitor 129 isdisposed upon the rear surface of the camera main body 100, and displaysphotographic images and actuation menus and the like. A recording medium132 is constituted by a data storage memory such as, for example, amemory card or the like. The calculation device 110 is capable ofstoring data for photographic images upon the recording medium 132, andreading out of data stored upon the recording medium 132. A buffermemory 127 is used for temporarily storing data during, before, andafter various types of image processing, image compression processing,and display data generation processing.

Since this single lens reflex electronic camera according to thisembodiment is particularly distinguished by the feature that thesensitivity of the range-finding element 109 is varied, accordingly itwill be explained with particular attention being given to its operationduring photography that includes focus detection processing. Varying thesensitivity of the range-finding element 109 is performed by varying, atleast, one of the time period T for accumulation of electric charge atthe range-finding element 109, and the amplification gain (G) for theaccumulation signal. FIG. 3 is a flow chart for explanation of the flowof photographic processing performed by the calculation device 110. Thecalculation device 110 repeatedly executes the processing of FIG. 3 whenthe camera power supply is turned ON.

In a step S301 of FIG. 3, the calculation device 110 sends a command tothe focus detection device 134 so as to set the initial values for thesensitivity of the range-finding sensor 109 (i.e. of its accumulationtime period and gain), and then the flow of control proceeds to a stepS302. In this step S302, the calculation device 110 sends a command tothe focus detection device 134 so as to perform focus detectioncalculation using AF (automatic focus adjustment), and then the flow ofcontrol proceeds to a step S303. By doing this, a defocus amount iscalculated using the detection signal that has been acquired by therange-finding element 109 whose sensitivity has been set to its initialvalue.

In a step S303, the calculation device 110 acquires detection andreliability information for the main photographic subject region, andthen the flow of control proceeds to a step S304. In concrete terms,along with issuing a command to the photometric unit 135 and performingAE (automatic exposure) calculation, it acquires an image signal fromthe area sensor 107 (i.e. a photoelectric conversion signal for eachpixel thereof). FIG. 4 is a figure showing an example of an image of thephotographic subject that is being imaged upon the area sensor 107, andFIG. 5 is a figure showing an example of an image acquired by the areasensor 107 by capturing the photographic subject image of FIG. 4.

The area sensor 107, for example, may have 22 pixels in the horizontaldirection (i.e. in the i direction) and 15 pixels in the verticaldirection (i.e. in the j direction). R (red), G (green), and B (blue)color filters are provided upon the photographic image surface of thearea sensor 107, in correspondence to the positions of the pixels. Inother words, a color filter of one of the colors R (red), G (green), andB (blue) is provided to each of the pixels. Since the area sensor 107acquires its image through these color filters, accordingly thedetection signal from the area sensor 107 includes color informationaccording to the RGB color system.

The calculation device 100 calculates the hue for each pixel accordingto a known method. The hue for each pixel [i,j] is denoted by Hue[i][j]. Here, i is an integer from 1 through 22, and j is an integer from 1through 15.

Using the hues Hue[i][j], the calculation device 110 divides thephotographic image into two regions: a background region (i.e. a regionin which the main photographic subject is not present), and anon-background region (i.e. a region in which the main photographicsubject is present). In concrete terms, it detects those pixel positionsat which the hue varies by more than a predetermined range, by scanningin order the rows of pixels in the image acquired by the area sensor 107from one end (for example from the upper edge of the image of thephotographic subject) in the direction of the other end (in this examplein the direction of the lower side of the photographic subject).

The above described pixel position detection is performed according tothe conditional expressions (1) and (2) below.

ABS(Hue[i][j]−Hue[i][1])<ThHue  (1)

Here, ABS( ) is a function that calculates the absolute value within theparentheses. And ThHue is a threshold value for decision that isdetermined in advance from experimental results.

M1[i][j−1]≠0  (2)

Here, M1[i][j] indicates whether or not the region that corresponds tothis pixel is included in the background. If M1[i][j] is not 0 then thispixel is included in the background, whereas if M1[i][j] is equal tozero then this pixel is not included in the background. In thisembodiment, it is supposed that the initial values of M1[i][1] in theupper edge pixel row are 1 (i.e. it is hypothesized that these pixelsare background pixels), whereas it is supposed that the initial valuesof M1[i][j] in the second through the 15th rows (2 ≦j≦15) are 0 (i.e. itis hypothesized that these pixels are not background pixels).

The calculation device 110 takes the pixel positions [i,j] for which theconditional expression (1) is not satisfied, as being the boundary thatdivides between the background region and the non-background region.And, when the conditional expression (1) is satisfied, the calculationdevice 110 makes the decision specified by the conditional expression(2), and increments the M1[i][j] of the subject pixel if the conditionalexpression (2) is satisfied.

By repeating the above decisions, the hues of the upper edge pixels(i.e. the pixels in the first row) that are hypothesized as being thebackground, and the hues of the pixels in the second and subsequentrows, are sequentially compared together, and the pixel positions in thepixel rows where the hue varies by more than the decision thresholdvalue for the first time, are taken as constituting the boundary betweenthe background region and the non-background region. FIG. 6 is a figureshowing an example of a situation in which the image of the photographicsubject is divided into two regions. The dark colored region at theupper side of the screen is the background region, while the lightcolored region at the lower side of the screen shows the non-backgroundregion (that is detected as being the main photographic subject).

The calculation device 110 may, for example, decide that the reliabilityis low, if no pixel row has been detected for which the hue varies bymore than the decision threshold value. If some pixel row is detectedfor which the hue varies by more than the decision threshold value, thenit is decided that the reliability is high.

In a step S304 of FIG. 3, the calculation device 110 determines thesensitivity of the range-finding sensor 109. In concrete terms, basedupon the signal values, in the detection signals from the range-findingsensor 109 (whose sensitivity is at its initial value) that has beenacquired in the step S302, from the pixels that correspond to the mainphotographic subject region detected in the step S303, it determinesthis sensitivity so that its signal value approaches close to a targetlevel. This target level is taken as being a level that is lower thanthe saturation level, but is as close as possible to the saturationlevel. In more concrete terms, the sensitivity is determined so that theaverage value of the signal values from the pixels that correspond tothe main photographic subject region becomes approximately the same asthe target level. It should be understood that the it would also beacceptable to arrange to determine the sensitivity so that the maximumvalue of the signal values from the pixels that correspond to the mainphotographic subject region becomes approximately the same as the targetlevel.

FIG. 7 is a figure showing an example of the relative positionalrelationship between the light reception area of the range-findingsensor 109 and the light reception area of the area sensor 107. Therange-finding sensor 109 of this embodiment has a light reception area109A that receives light at the left side of the screen, a lightreception area 109B that receives light at the middle of the screen, anda light reception area 109C that receives light at the right side of thescreen. In this case the calculation device 110 determines thesensitivity of the line sensor having this light reception area 109Athat corresponds to the main photographic subject region, based upon thesignal values from a pixel group X upon the line sensor that overlapswith the above described main photographic subject region.

In a step S305, the calculation device 110 sends the sensitivityinformation and the reliability information that have been determined inthe step S304 to the focus detection device 134 and performs focusdetection calculation for AF (automatic focus adjustment), and then theflow of control proceeds to a step S306. Due to this, the focusdetection device 134 changes the sensitivity of the range-finding sensor109 to the value that has been commanded from the calculation device110, and the defocus amount is calculated using the detection signalacquired by the range-finding element 109 whose sensitivity has been setafter this change.

It should be understood that, if reliability information has beenreceived to the effect that the reliability is low, then the focusdetection device 134 calculates the defocus amount using a detectionsignal that has been acquired by the range-finding element 109 whosesensitivity is set to the initial value described above.

In the step S306, the calculation device 110 makes a decision as towhether or not the release half press switch has been actuated. If anactuation signal has been inputted from the release half press switch130, then the calculation device 110 reaches an affirmative decision inthis step S306 and the flow of control proceeds to a step S307. On theother hand, if no actuation signal has been inputted from the releasehalf press switch 130, then the calculation device 110 reaches anegative decision in this step S306 and the flow of control is returnsback to the step S303, and the processing described above is repeated.

In the step S307, the calculation device 110 sends lens controlinformation such as a shift amount for the optical system 152 for focusadjustment or a drive command or the like to the photographic lens 150via the communication control unit 136, and then the flow of controlproceeds to a step S308. By the lens drive mechanism (not shown in thefigures) within the photographic lens 150 shifting the optical system152 along the direction of the optical axis according to this lenscontrol information, the photographic lens 150 is focused upon the mainphotographic subject 101.

In the step S308, the calculation device 110 makes a decision as towhether or not the release full press switch has been actuated. If anactuation signal has been inputted from the release full press switch131, then the calculation device 110 reaches an affirmative decision inthis step S308 and the flow of control proceeds to a step S309. On theother hand, if no actuation signal has been inputted from the releasefull press switch 131, then the calculation device 110 reaches anegative decision in this step S308 and the flow of control is returnsback to the step S303, and the processing described above is repeated.

In the step S309, the calculation device 110 sends a command to themirror control unit 138, so as to start the up driving of the quickreturn mirror 103. Moreover, the calculation device 110 sends a commandto the shutter control unit 137 and drives a curtain of the shutter 113to open it, and then the flow of control proceeds to a step S310.

In the step S310, the calculation device 110 causes the image sensor 121to accumulate electrical charges for photography, and then the flow ofcontrol proceeds to a step S311. And, after the closing of the shutter113 that will be described hereinafter, the calculation device 110discharges the accumulated electrical charges.

In the step S311, the calculation device 110 sends a command to theshutter control unit 137, and drives the curtain of the shutter 113 toclose it. Moreover, the calculation device 110 sends a command to themirror control unit 138 to start the down driving of the quick returnmirror 103, and then the flow of control proceeds to a step S312.

Furthermore, the calculation device 110 performs predetermined imageprocessing upon the image that has been captured, and records the imagedata after image processing upon the recording medium 132. And thecalculation device 110 sends a command to the display image generationcircuit 128, so as to cause the image that has been photographed to bereplay displayed upon the liquid crystal monitor 129. With this, thesequence for photographic processing terminates.

In the step S312, the calculation device 110 makes a decision as towhether or not the camera power supply continues to be ON. If the cameramain switch (not shown in the figures) is not actuated to OFF andmoreover, during an episode of non-actuation, a timer has not timed up,then the CPU 101 reaches an affirmative decision in this step S312 andthe flow of control returns to the step S303. On the other hand, if themain switch is actuated to OFF or the timer has timed up during anepisode of non-actuation, then the calculation device 110 reaches anegative decision in this step S312 and turns the supply of power to thecamera OFF, and then the processing of FIG. 3 terminates.

According to the embodiment explained above, the following advantageousoperational effects are obtained.

(1) It is arranged for the calculation device 110 of the camera toextract the region that includes the main photographic subject 101 fromthe image information obtained in two dimensions by the area sensor 107for photometry, and to determine the sensitivity of the line sensor (therange-finding sensor 109) including the light reception area 109A thatcorresponds to this extracted region, based upon the signal values froma pixel group X of this line sensor. Due to this, it is possible toacquire the pair of images for focus detection with a sensitivity thatis appropriate to the luminance of the main photographic subject 101,without receiving any influence from the luminance of the backgroundregion other than the main photographic subject. In other words, it ispossible to control in an appropriate manner the accumulation ofelectrical charges by the range-finding sensor 109 used for focusdetection, that is a storage type image sensor. As a result, it ispossible to obtain signal values of an appropriate level from therange-finding sensor 109, and thus to obtain the defocus amountcorrectly.

(2) In addition to (1) above, by eliminating the line sensors such asthe light reception areas 109B and 109C that do not correspond to themain photographic region from the subject of focus detectioncalculation, it is possible to alleviate the burden of calculation.

(3) It is arranged to decide upon the boundary between the mainphotographic subject region and other regions by deciding, between theupper edge pixel and pixels from above towards below of the imageinformation from the area sensor 107, whether or not the difference ofhue is within the predetermined decision threshold value. Generally, thepossibility is high that the upper edge of the image of the photographicsubject is the background (i.e. is not included in the main photographicsubject), and the possibility is high that image information of the samehue as the background is part of the background. Due to this, it ispossible to distinguish between the background region and other regions(i.e. regions for which there is a possibility that they are includedwithin the main photographic subject 101) in a simple manner. It shouldbe noted that the boundary between the main photographic subject regionand other regions can be decided by deciding, between adjacent pixels ofthe picture information from the area sensor 107 from above towardsbelow, whether or not the difference of hue is within a predetermineddecision threshold value.

(4) Since the area sensor 107 is provided separately from the imagesensor 121 for photography, and its pixel number is made to be smallerthan the number of pixels of the image sensor 121 (for example tens ofmillions of pixels), accordingly it is possible to make the structuremore compact, as compared to the case of providing an area sensor 107that is the same as the image sensor 121. Moreover, by using the imageinformation that is obtained by the area sensor 107 for photometry, itis possible to determine the sensitivity of the range-finding sensor 109at the time point of photometry, before the image sensor 121 capturesits image.

(5) Since the range-finding sensor 109 is provided separately from thearea sensor 107, and is made as a line sensor whose pixel number issmaller than the number of pixels of the area sensor 107, accordingly itis possible to make the structure more compact, as compared to the caseof providing a range-finding sensor 109 that is the same as the areasensor 107.

VARIANT EMBODIMENT #1

In the above explanation, an example was described in which, whendividing the image information from the area sensor 107 into two groups,the boundary for division was decided by deciding whether or not thechange of hue was within a predetermined hue decision threshold value.Instead of this, it would also be acceptable to arrange to decide uponthe boundary for division by deciding whether or not the change ofluminance is within a predetermined luminance decision threshold value.

VARIANT EMBODIMENT #2

Moreover, it would also be acceptable to arrange to decide upon theboundary for division by deciding upon both the hue and the luminance.

VARIANT EMBODIMENT #3

In the above explanation, when deciding upon the boundary for division,it was arranged to compare together the hue or the luminance between theupper edge pixel and pixels from the upper edge towards the lower edgeof the image information from the area sensor 107, thereof. However,instead of this, it would also be acceptable to arrange to make acomparison between the right edge pixel and pixels from the right edgetowards the left edge of the image information from the area sensor 107,or between left edge pixel and pixels from the left edge towards theright edge of the image information from the area sensor 107.

It should be noted as mentioned above that it would also be acceptableto arrange to make a comparison between adjacent pixels from the areasensor 107 from the right edge of the image information towards the leftedge thereof, or between adjacent pixels from the area sensor 107 fromthe left edge of the image information towards the right edge thereof.

VARIANT EMBODIMENT #4

Although an example has been shown and explained in which there was onlya single line sensor having a light reception area corresponding to themain photographic subject region, the present invention can also beapplied to a case in which a plurality of sensors are present that havelight reception areas corresponding to the main photographic subjectregion. In this case, for each line sensor, it will be sufficient todetermine the sensitivities of the line sensors based upon the signalvalue from a pixel group that overlaps the main photographic subjectregion; it is not necessary to adjust the sensitivities between theplurality of line sensors.

VARIANT EMBODIMENT #5

Although an example of an electronic camera has been explained, thepresent invention may also be applied to a film camera.

The above described embodiments are examples, and various modificationscan be made without departing from the scope of the invention.

1. A camera, comprising: a first sensor of a storage type that has aplurality of pixels; a focus detection unit that detects a focusadjustment state of a photographic optical system based upon a detectionsignal from the first sensor for a photographic subject; a second sensorthat acquires an image of the photographic subject; an extraction unitthat extracts a main photographic subject region from image informationacquired by the second sensor; and a control unit that controlsaccumulation of electrical charge by the first sensor, based upon valuesoutputted from pixels of the first sensor that correspond to the mainphotographic subject region.
 2. A camera according to claim 1, whereinthe extraction unit extracts the main photographic subject region bydeciding whether or not at least one of a hue and a luminance isapproximately equal to each other between an upper end region andanother region in a direction from above towards below in the imageinformation.
 3. A camera according to claim 1, wherein the first sensoris constituted by a line sensor.
 4. A camera according to claim 3,wherein the focus detection unit performs focus detection calculation bya phase detection method in which a defocus amount is calculatedaccording to a gap between a pair of images given by the detectionsignal of the line sensor.
 5. A camera according to claim 1, wherein thesecond sensor is constituted by an area sensor for photometry.
 6. Acamera according to claim 1, wherein the control unit controlsaccumulation of electrical charge by the first sensor, so that outputvalues of pixels of the first sensor that correspond to the mainphotographic subject region that has been extracted approach apredetermined target level.
 7. A camera according to claim 6, whereinthe predetermined target level is a level that is lower than asaturation level and is close to the saturation level.
 8. A camera,comprising: a first sensor of a storage type that has a plurality ofpixels; a focus detection unit that detects a focus adjustment state ofa photographic optical system based upon a detection signal from thefirst sensor for a photographic subject; a second sensor that acquiresan image of the photographic subject; an extraction unit that extracts amain photographic subject region from image information acquired by thesecond sensor; a control unit that controls accumulation of electricalcharge by the first sensor, based upon values outputted from pixels ofthe first sensor that correspond to the main photographic subjectregion; and a third sensor that acquires an image of the photographicsubject for recording.
 9. A camera according to claim 8, wherein thecontrol unit performs control of electric charge accumulation by thefirst sensor and acquisition of an image of the photographic subject bythe second sensor, before performing acquisition of an image of thephotographic subject with the third sensor.
 10. A camera control method,comprising: capturing an image; extracting a main photographic subjectregion from the captured image; and determining a sensitivity of arange-finding sensor having a plurality of pixels, based upon outputs ofpixels of the range-finding sensor that correspond to the extracted mainphotographic subject region.